Tau, a measure of how much sunlight cannot penetrate the atmosphere, rose to a high of 1.5 on the afternoon of sol 418, but the opacity of the atmosphere has since dropped off. Energy output from Spirit's solar panels is up as of sol 420, indicating that some cleaning of dust off of the solar arrays may have occurred naturally.

As Spirit and Opportunity are the first solar-powered vehicles on the surface of Mars during the dust storm season, this is a learning experience.

There are likely large transient dust storm events that reduce solar energy due to dust deposition on the solar arrays and blocking some sunshine, but also may sometimes raise energy levels by cleaning dust from arrays, possibly by winds associated with dust storms. The impact on other rover systems, such as cameras, will also be closely monitored.

Sol-by-sol summaries:

On sol 416, which ended on March 5, 2005, Spirit awoke around 4 a.m. local solar time at Gusev Crater to start its alpha particle X-ray spectrometer and use a communication window with the Mars Odyssey orbiter passing overhead. Later, Spirit did a three-hour grind with its rock abrasion tool, digging about 7 millimeters (0.27 inch) into Watchtower. Spirit then placed the alpha particle X-ray spectrometer into the rock abrasion tool hole for an overnight integration.

On sol 417, Spirit gathered images of the rock abrasion tool hole with the microscopic imager, performed a variety of remote-sensing observations, and then placed the Moessbauer spectrometer in the hole for an overnight integration.

On sol 418, Spirit continued the Moessbauer spectrometer integration and acquired remote-sensing data. A regional dust storm caused tau the reach a new high if 1.5 in the afternoon and reduced solar energy for the day to roughly 350 watt-hours. After the dust storm, Spirit's front hazard-avoidance camera showed signs of dust contamination similar to that seen earlier on Opportunity's rear hazard-avoidance camera.

On sol 419, Spirit completed remote-sensing observations, including imaging to learn more about the contamination on the front hazard-avoidance camera. Slight mottling is visible in images from both eyes of the stereo camera. It is not enough to affect use of the camera or to have any direct impact on rover operations, but understanding how it happened might help the rover team minimize future occurrences.

Spirit then moved backwards about 1 meter (3 feet) from Watchtower to use mast-mounted instruments for observing that rock. After that, it starting to drive toward the soil target Paso Robles. However, the planned 14-meter (46-foot) drive ended after just 1 meter (3 feet) due to a software sequence ordering issue.

On sol 420, Spirit drove 7 meters (23 feet) of a planned 14 meters (46 feet) towards Paso Robles. The drive ended prematurely due to a problem in visual odometry, which is part of the software that enables the rover to drive autonomously. Energy output from the solar array rose dramatically, to more than 600 watt-hours. In part, this is due to a favorable northerly tilt of the rover, which points the solar arrays toward the Sun. Also, tau is going back down, but it is possible that some cleaning event occurred that reduced the dust on the solar panels.

On sol 421, Spirit drove 7 meters (23 feet) and arrived close to the Paso Robles target. Spirit still needs another few meters to get into position to use the instruments on its robotic arm. Solar energy continues to be very high: more than 700 watt-hours. The last time Spirit had this much energy was around sol 80.

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